This invention relates in general to seals and more particularly to a self-venting seal for use with a bearing and to an assembly including such a seal.
Several basic mounting arrangements exist for the wheel bearings installed in automobiles of current manufacture. In perhaps the most common, a pair of angular bearings, such as single row tapered roller bearings, are positioned between a dead spindle and a rotatable hub, the outer races of the two bearings being fitted to the hub and the inner races around the spindle. The dead spindle may be on the steering knuckle of a rear wheel drive automobile, or on the rear axle or rear swing arm of a front wheel drive automobile. In another common arrangement used at the front wheel locations of front wheel drive automobiles, again two rows of rolling elements are employed, but the outer races remain stationary in the steering knuckle, while the inner races revolve with a drive flange that is coupled to a driven axle through a universal joint. In still another arrangement that is common to the rear wheel locations of rear wheel drive automobiles, one single row bearing is employed at each wheel, it having its outer race fitted to the axle housing and its inner race around the axle. Of course, many variations of these basic arrangements exist.
Irrespective of the bearing arrangement, the bearings are confined to a space or cavity that is isolated from the surrounding atmosphere by a seal, which is typically a lip-type seal. The seal retains lubricants within the bearing cavity and further prevents contaminants from entering the cavity.
The typical seal used with automotive wheel bearings has a metal case, which fits into a bearing housing, such as a hub or steering knuckle, or into the outer race of the bearing itself, and an elastomeric lip that bears against a wear surface which may be on or adjacent to the inner race of the bearing. The seal lip forms a barrier to the passage of fluid along the wear surface as the inner race rotates relative to the seal and outer race or vice-versa. The lip is somewhat delicate, and to prevent it from being damaged during operation of the bearing and to orient it properly for sealing efficiency, the lip turns axially inwardly toward the cavity in which the bearing is contained. Thus, a moderate increase in pressure within that cavity will impose a radially directed force on the lip, causing the lip to bear with greater force against the wear surface. This in turn causes the seal to heat up and deteriorate during operation. The elevated temperatures further cause the lubricant in the region of the seal to lose its effectiveness, which in turn compounds the problem. A substantial increase in pressure within the bearing cavity may have more damaging consequences, for a large pressure differential may cause the seal to actually blow out of the bearing cavity, in which case the lubricant will be lost and contaminants may enter the bearing cavity.
Perhaps braking is the most common cause of pressure increases within the bearing cavities of wheel bearings. In this regard, the bearings and the cavities in which they are isolated are invariably located next to brake drums or disks. Repeated applications of the brake cause the drums or disks to heat up and some of the heat is conducted into the hub or drive flange on which the bearings are mounted. This, is particularly true of automobiles of current manufacture, for the drive trains in these vehicles have extremely low drag and thereby shift more of the braking effort to the brakes themselves. Moreover, the wheels, hubs, drive flanges, and other wheel components found on automobiles of current manufacture have less mass than their earlier counterparts and therefore less area from which to dissipate the heat. As a consequence, more heat soaks back into the bearing cavity and that cavity operates at a higher temperature and pressure.
Some bearing arrangements have fittings through which a lubricant can be introduced under pressure into the bearing cavity. These arrangements are further susceptible to developing excessive pressures in their bearing cavities during the addition of lubricant to the cavities.
Heretofore vents have been incorporated into seals that have been utilized with bearings, but these vents have for the most part been confined to larger seals of the type used at the journals of railcar axles. The seals used with automotive wheel bearings are considerably smaller, and very little free area exists on such seals for accommodating an operative vent.